1. Technical Field
The present invention generally relates to ferromagnetic silicon. More particularly, the present invention relates to ferromagnetic silicon with a Curie temperature above room temperature.
2. Background Information
Utilizing the spin of the electron in semiconductor devices holds great potential to provide high-speed device structures. The integration of ferromagnetism into these device structures is needed to couple to electron spin. Diluted magnetic semiconductors (DMS) have been demonstrated as a successful method for integrating ferromagnetism through doping of a semiconductor crystal with an additional transition metal impurity such as manganese (Mn).
Epitaxially grown Group III-V semiconductors such as Ga1−xMnxAs, have achieved ferromagnetism with Curie temperatures up to 110 K for (x≈5%) and have been successfully utilized as spin aligners in spin-LED devices. This success has motivated the search for Group-IV-based DMS materials with high Curie temperatures, due to their compatibility with conventional integrated circuits. Recently, an epitaxially grown single crystal of MnxGe1−x (x—3.5%) achieved a magnetically ordered phase from a long-range ferromagnetic interaction at 116 K, epitaxially grown thin films of CexSi1−x (x=0.5%) produced a material with a magnetic susceptibility that displayed spin glass-like behavior around 40 K, and epitaxially grown MnxSi1−x (x=5%) thin films produced a material with an anomalous Hall effect (due to internal magnetization) around 70 K. These findings are also supported by theoretical calculations that have predicted ferromagnetic ordering in Group-IV semiconductors.
Ion implantation has also been utilized to achieve ferromagnetism in semiconductor crystals, and it is an attractive technique, since it is routinely used in the manufacturing of integrated circuits. For example, three atomic percent Mn-implanted GaN and GaP achieved Curie temperatures of 270 and 250 K, respectively. Furthermore, ion implantation is attractive for a silicon-based DMS, since Mn concentrations of about one atomic percent (˜1020 cm−3 for Si) would be needed, exceeding the solubility limit of Mn in Si (˜1016 cm−3 at 1000 degrees Celsius).
Somewhat surprisingly, the fabrication of a silicon-based DMS via ion implantation of manganese has not been reported. Only recently, have the structural properties of Mn-ion implantation into Si been studied. Missing from both the epitaxially grown (Mn, Ce)-doped silicon thin-film studies and the Mn-ion implantation into Si studies is a direct measure of ferromagnetic properties and their dependence upon temperature.
Thus, a need exists for a diluted magnetic semiconductor that is easily incorporated into modern semiconductor production and useful in applications at and above room temperature.